In split phase motors it is necessary to provide an auxiliary or starting winding in the main winding circuit which will produce the required initial torque characteristics for starting the motor under load and bringing the motor up to an operating speed at which the main winding alone develops an adequate running torque, at which speed the starting winding circuit is opened. The mechanism for making and breaking the starting winding circuit consists of a stationary electrical switch which is mechanically engaged by a centrifugal speed-responsive rotary device which is mounted on the motor shaft. When the motor is rotating at a predetermined operating speed, the rotary device is withdrawn by centerifugal force from engagement with the normally open stationary switch and the starting winding circuit is inoperative. If the rotation of the motor ceases or is reduced below a critical value, the centrifugal forces acting on the rotary device are reduced and the rotary device engages the stationary switch to close the starting winding circuit. For a more detailed description of the forms and operation of such prior art switching arrangements, reference is made to my U.S. Pat. Nos. 2,616,682 and 3,272,950.
The aforementioned patents discuss and describe the critical nature of the forces involved in obtaining uniformity of operation in such starting winding devices and the variables which have to be considered and for which appropriate compensation has to be provided in design and arrangement if an improved standard of performance is to be achieved.
With the advent of high density electrical motors which impress higher electrical values on the winding circuits, it becomes more important to obtain high force or energy levels for opening of the switch contacts while maintaining a uniform and constant contact-closing force which will not unduly oppose and negate the opening force.